The present invention relates in general to an optical type record carrier body and, in particular, to a radiation-sensitive record carrier body which is utilized as a stamper structure for manufacturing an optical type data recording disk.
In order to stabilize a servo-tracking operation and to improve recording density, it is known in the prior art to form an indentation which serves as a track of a predetermined shape in a recording medium such as an optical disk in which information is recorded digitally in accordance with an energy beam such as a laser beam radiated thereupon. Such a track or a pre-track is formed on the surface of a recording layer of an optical disk as either a protuberance or a groove, and in the form of either a continuous spiral or a discontinuous concentric pattern. The servo-tracking operation is carried out in accordance with a difference between reflectances of the track portion of the optical disk and the remaining flat portion thereof.
In order to manufacture a read/write optical disk having such a pre-track on which desired information may be digitally recorded or from which such information may be digitally reproduced by a user, a stamper having a surface configuration conforming to the pre-track must first be prepared. Conventionally, a master or original disk having a track is prepared Then, an electroforming technique, for example, is used to prepare a stamper structure having a surface pattern opposite to that of the original disk. Using this stamper, optical disks having identical surface configurations, that is, tracks transferred thereto from the stamper, which are the same as that of the original disk, are manufactured. The optical disks are prepared by injection molding, compression molding or pouring of an organic resin, or by curing an ultraviolet curing resin.
Conventionally, the stamper structure with a continuous spiral pre-groove or track is manufactured as follows. A chrominum film is formed on a top surface of a transparent substrate comprising disk-shaped glass (of, e.g., 300 mm diameter). A photoresist material is applied by a spinner or the like to the surface of the chromium film, thus forming a photoresist film. The substrate having the photoresist film formed thereon in the manner described above is then rotated at a predetermined speed. A laser beam is then focused to radiate the photoresist film of the rotating substrate so as to form a beam spot of 4,000 .ANG. or 4 .mu.m in diameter. This laser beam is moved at a constant feed speed along the radial direction of the rotating disk-shaped substrate. When irradiation by the laser beam is completed, the structure exposed to the laser beam is etched, thereby obtaining an original disk which has a continuous spiral pre-groove. The track may alternatively comprise a projection or ridge, depending on the type of photoresist material. An electrode is deposited on the original disk, and the obtained structure is subjected to electroforming. A disk structure having a transferred indentation of the original disk is separated therefrom to form a stamper.
However, in the prior art, it is very difficult to uniformly form the spiral track portion to have a width of 1 .mu.m and a depth of 0.08 .mu.m over the entire surface of the disk-shaped structure of 300 mm in diameter. In general, when the photoresist material is applied to the substrate to form a photoresist film having a thickness of the order of microns, the photoresist film tends to partially peel off from the disk-shaped substrate. As a result, uniformity of the film cannot be expected. In particular, when the photoresist film is formed to have a thickness of the order of submicrons, the photoresist material must be diluted before being applied to the surface of the substrate. As a result, the uniformity of the photoresist film is further degraded, and irregular development and etching occur. Nonuniformity occurring at the beginning of the stamper manufacturing process results in a definite fault in the optical disk. In this manner, a spiral track having the dimensions described above over the entire surface of the substrate of the optical disk is extremely difficult to form.
Further, according to the prior art stamper, when the photoresist film is separated from the stamper, the photoresist film may partially remain on the stamper due to baking or the like. In addition to this, since the stamper structure is prepared from an original disk, the manufacturing process involves a large number of steps and is complex, requiring further improvements.